Objective: To evaluate mortality and morbidity in a large cohort of twin pregnancies according to chorionicity. We aimed to estimate the optimal time of delivery.
Design: Historical cohort design. Setting Two teaching hospitals.
Population: Twin pregnancies delivered in the University Medical Centre, Utrecht, and the St Elisabeth Hospital, Tilburg (1995-2004), The Netherlands (n = 1407).
Methods: Pregnancy outcomes were documented according to chorionicity. Mortality >/=32 weeks was reviewed carefully with special attention to antenatal fetal monitoring, autopsy and placental histopathology to find an explanation for adverse outcome.
Main outcome measures: Perinatal mortality and morbidity in monochorionic (MC) and dichorionic (DC) twins.
Results: Perinatal mortality was 11.6% in MC twin pregnancies and 5.0% in DC twin pregnancies. After 32 weeks, the risk of intrauterine death (IUD) was significantly higher in MC twins than in DC twins (hazard ratio 8.8, 95% CI 2.7-28.9). In most of these cases of IUD, no antenatal signs of impaired fetal condition had been present. Median gestational age was 1 week longer in DC twins than in MC twins, and the mean birthweight was 221 g higher. Severe birthweight discordancy (>20%) occurred more often in MC twins than in DC twins (OR 1.23, 95% CI 0.97-1.55). The incidence of necrotising enterocolitis (NEC) was higher in MC twins, after adjustment for age and weight at birth (OR 4.05, 95% CI 1.97-8.35). There was a trend towards higher neuromorbidity in MC twins.
Conclusions: This is the largest cohort study of twin pregnancies evaluating outcome according to chorionicity thus far. MC twins are at increased risk for fetal death (even at term), NEC and neuromorbidity. Current antenatal care is insufficient to predict and prevent this excess perinatal mortality and morbidity. Planned delivery at or even before 37 weeks of gestation seems to be justified for MC twins.